musescore/MuseScore — pull request #1557 by MarcSabatella (2014-12-20 00:55:49+00:00)
Title: fix #41766: use double sharp/flat where appropriate when transposing

In 1.3, we used double sharp/flat on notes when transposing via Concert Pitch toggle, I see no reason not to continue doing so. We should also use it for chord symbols now that we support this. Unless we wanted to add a style option or staff property to control this - along, perhaps, with some sort of control over key simfplification (turning C# major into Db). If so, then all the places I turned "false" to "true" here would become references to that style option. Or maybe a new function that encapsulates that.

But unless we do decide to go with an option to control this, I think we should use double flat/sharp for both notes and chord symbols. User can always change the spelling manually if he wants.